This invention relates generally to pressure measuring systems, and more particularly, to an arrangement for measuring the pressure in cylindrical cavities by measuring the circumferential expansion of the cylindrical cavity by means of electrical pickups which are responsive to variations in length in at least one axis.
U.S. Pat. No. 3,937,087 describes an arrangement wherein a strain detector is mounted on the circumference of a fuel injection line of an internal combustion engine for producing a pressure-time history of the fuel injection cycle. In the known system, stresses in the fuel injection line which are not caused by pressure variations within the line are prevented from disturbing the pressure measurement by the provision of a steel housing which firmly surrounds a portion of the fuel injection line, and which extends on either side of the location of the strain detector. Such a housing contains an annular cavity which surrounds the strain detector.
It is a problem with known pressure monitoring systems that the monitoring of circumferential expansion of a fuel line in response to internal pressure is disturbed by bending and longitudinal stresses which result from the running of the engine. Such disturbances, therefore, result from vibratory motions and forces which occur during operation of the engine, and interfere with the measurement of circumferential elongations which result from pressure variations within the cylindrical fuel line.
It is, therefore, an object of this invention to provide an arrangement for measuring the pressure within a cylindrical cavity, and which provides improved suppression of signals which result from other forces acting upon the cylindrical cavity.
It is further object of this invention to provide a pressure measurement system which compensates for disturbances which affect circumferential expansion of the cylindrical cavity by determining longitudinal elongations which result from flexure or tensile stresses.